The most consistent aspect of therapy for pulmonary diseases such as, for example, cystic fibrosis (CF), is limiting and treating the lung damage caused by thick mucus and infection with the goal of maintaining quality of life.
Cystic fibrosis is a life-threatening, inherited disorder caused by an abnormality in the cystic fibrosis transmembrane conductance regulator (CFTR) and characterized by chronic progressive lung disease. Abnormal function of CFTR (and other ion channels) leads to inspissated static mucus in the lungs and a situation where mucociliary clearance and other antimicrobial defenses are damaged. The damage is so extensive that persistent infection by a predictable set of pathogens, especially Pseudomonas aeruginosa, and a concomitant chronic neutrophilic inflammatory response are characteristic consequences which are usually fatal. Pilewski, J. M. and Frizzell, R. A. (1999) Physiol. Rev. 79 (suppl. 1), 5215-5255; Chmiel, J. F. and Davis. P. B. (2003) State of the Art: Why do the lungs of patients with cystic fibrosis become infected and why can't they clear the infection? Resp. Res. 4, 8-20; Gibson, R. L., Burns, J. L. and Ramsey, B. W. (2003) Pathophysiology and management of pulmonary infections in cystic fibrosis. Am. J. Respir. Crit. Care Med. 168, 918-951.
P. aeruginosa grows in microcolonics with biofilm-like characteristics in the hypoxic environment of such stationary mucus where the bacterial cells elaborate a quorum-sensing system to control gene expression specifically for growth as a biofilm. Singh, P. K., Schaefer, A. L., Parsek, M. R., Moninger, T. O., Welsh, M. J. and Greenberg, E. P. (2000) Quorum-sensing signals indicate that cystic fibrosis lungs are infected with bacterial biofilms. Nature 407, 762-764; Parsek, M. R. and Greenberg, E. P. (2000) Acyl-homoserine lactone quorum sensing gram-negative bacteria: A signaling mechanism involved in associations with higher organisms. Proc. Nat. Acad. Sci. 97, 6789-6793. Observation of tissue samples from cystic fibrosis patients indicates that the P. aeruginosa is predominantly intraluminal, localized in hypoxic mucopurulent masses. Worlitzsch, D., Tarran, R., Ulrich, M., Schwab, U., Cekici, A., Meyer, K. C., Birrer, P., Bellon, G., Berger, J., Weiss, T., Botzenhart, K., Yankaskas, J. R., Randell, S., Boucher, R. C. and Doring, G. (2002) Effects of Reduced Mucus Oxygen Concentrations in Airway Pseudomonas infections of Cystic Fibrosis Patients. J. Clin. Invest. 109, 317-325. This environment may include a matrix composed of alginate or other exopolysaccharides from mucoid bacteria, mucins from lung epithelial cells and DNA from damaged leukocytes. Costerton, J. W., Stewart, P. S., and Greenberg, E. P. (1999) Bacterial Biofilms: A Common Cause of Persistent Infections, Science 284:1318-1322. Alginate production by P. aeruginosa is actually stimulated in such hypoxic conditions, converting non-mucoid versions to mucoid. Worlitzsch, D., Tarran, R., Ulrich, M., Schwab, U., Cekici, A., Meyer, K. C., Birrer, P., Bellon, G., Berger, J., Weiss, T., Botzenhart, K., Yankaskas, J. R., Randell, S., Boucher, R. C. and Doring, G. (2002) Effects of Reduced Mucus Oxygen Concentrations in Airway Pseudomonas infections of Cystic Fibrosis Patients. J. Clin. Invest. 109, 317-325; Sabra W., Kim E. J., Zeng A. P. (2002) Physiological responses of Pseudomonas aeruginosa PAO1 to oxidative stress in controlled microaerobic and aerobic cultures. Microbiology 148, 3195-3202.
The biofilm-like mode of growth results in a difficult challenge for antibiotic therapy. For aminoglycosides, slow penetration and lack of activity against cells in a slow growth phenotype are particularly important. Mendelman, P. M. et al., “Aminoglycoside Penetration, Inactivation, and Efficacy in Cystic Fibrosis Sputum,” Am. Rev. Respir. Div. 1985, 132(4), 761-5; Hunt, B. E. et al. “Macromolecular Mechanisms of Sputum inhibition of Tobramycin Activity,” Antimicrob. Agents Chemother., 1995, 39(1), 34-9; Chambless, J. D., Hunt, S. M. and Stewart, P. S. (2006). A three-dimensional computer model of four hypothetical mechanisms protecting biofilms from antimicrobials. Appl Environ Microbiol 72, 2005-13. To make matters worse, subinhibitory levels of aminoglycosides help to induce biofilm formation. Drenkard, E. and Ausubel, F. M. (2002) Pseudomonas biofilm formation and antibiotic resistance are linked to phenotypic variation. Nature 416, 740-743; Hoffman, L. R., D'Argenio, D. A., MacCoss, M J., Zhang, Z., Jones, R. A. and Miller, S. I. (2005). Aminoglycoside antibiotics induce bacterial biofilm formation. Nature 436, 1171-1175. One approach to increase efficacy in this situation has been direct administration of antibiotics to the lungs via inhalation. However, because of the small size and charged nature of these drugs, they are rapidly removed from the lungs after inhalation, limiting the amount of time they remain at a concentration above the effective minimum inhibitory concentration. P. P. H. LeBrun et al: Pharmcokinetic modeling of tobramycin after high dose inhalation in patients with cystic fibrosis. In: “Optimization of antibiotic inhalation therapy in cystic fibrosis” Ph.D. thesis, Rijksuniversiteit Groningen, 2001, Chapter 7; J. S. Patton, C. S. Fishburn, and J. G. Weers. The lungs as a portal of entry for systemic drug delivery. Proc. Am. Thor. Soc. 1:338-344 (2004). The charged nature of many of the antibiotics used in these applications also inhibits their penetration of the predominantly anionic biofilms that form in many pulmonary diseases.
Pneumonia is an illness of the lungs and respiratory system in which the alveoli (microscopic air-filled sacs of the lung responsible for absorbing oxygen from the atmosphere) become inflamed and flooded with fluid. Pneumonia can result from a variety of causes, including infection with bacteria, viruses, fungi, or parasites. Pneumonia may also occur from chemical or physical injury to the lungs, or indirectly due to another medical illness, such as lung cancer or alcohol abuse.
Antibiotics are given whenever pneumonia is suspected or to treat bacterial infections associated with cystic fibrosis resulting in a decline in lung function. Antibiotics are often chosen based on information about prior infections. Many bacteria common in pulmonary distress are resistant to multiple antibiotics and require weeks of treatment with intravenous antibiotics such as amikacin, vancomycin, tobramycin, meropenem, ciprofloxacin, and piperacillin. This prolonged therapy often necessitates hospitalization and insertion of a more permanent IV such as a PICC line or Port-a-Cath. Inhaled therapy with antibiotics such as tobramycin and colistin is often given for months at a time in order to improve lung function by impeding the growth of colonized bacteria. Pai V B, Nahata M C. Efficacy and safety of aerosolized tobramycin in cystic fibrosis. Pediatr Pulmonol. 2001 October; 32(4):314-27. Review; Westerman E M, Le Brun P P, Touw D J, Frijlink H W, Heijerman H G. Effect of nebulized colistin sulphate and colistin sulphomethate on lung function in patients with cystic fibrosis: a pilot study. J Cyst Fibros. 2004 March; 3(1):23-8. Oral antibiotics such as ciprofloxacin or azithromycin are sometimes given to help prevent infection or to control ongoing infection. Hansen C R, Pressler T, Koch C, Hoiby N. Long-term azithromycin treatment of cystic fibrosis patients with chronic Pseudomonas aeruginosa infection; an observational cohort study. J Cyst Fibros. 2005 March; 4(1):35-40. Some individuals spend years between hospitalizations for antibiotics, while others require several antibiotic treatments each year.
Improved antibiotic compositions are needed that overcome the problem of biofilm penetration due to the oppositely charged multicationic drug and polyanionic biofilm.